How to make Network_Mode : "host" work in docker-compose.yml file

I am trying to execute a “docker-compose up” command. Please find below my docker-compose file. I tried with network_mode: “host” but it doesn’t work. I am on Linux OS. request you to let me know if I am making any blunder.

version: '3.6'
services:
   mongo:
      image: "mongo:latest"
      container_name: ohif-mongo
       ports:
         - "27017:27017"

   viewer:
      image: ohif/viewer:latest
      container_name: ohif-viewer
      ports:
        - "3030:3000"
      network_mode: "host"   # please make note of the alignment
      links:
         - mongo
      environment:
         - MONGO_URL=mongodb://mongo:27017/ohif
      extra_hosts:
         - "pacsIP:172.xx.xxx.xxx"
      volumes:
         - ./dockersupport-app.json:/app/app.json

after execution, I get the below error

ERROR: for 8f4c3de7e3a3_ohif-viewer  Cannot create container for service viewer: conflicting options: host type networking can't be used with links. This would result in undefined behavior
 ERROR: for viewer  Cannot create container for service viewer: conflicting options: host type networking can't be used with links. This would result in undefined behavior

I don’t know why the error message is displayed twice. Not sure whether this is expected

Second, when I change the alignment of network_mode: “host” (by 1/2 spaces)

  ports:
        - "3030:3000"
        network_mode: "host"   # please see the change in alignment now
      links:
         - mongo

I get the below error message

ERROR: yaml.parser.ParserError: while parsing a block mapping
 in "./docker-compose.yml", line 10, column 5
expected <block end>, but found '<block mapping start>'
 in "./docker-compose.yml", line 14, column 6

How can I start the container with network=host mode?

Source: StackOverflow